An ink jet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes dot locations, dot positions, or pixels. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times corresponding to the pattern of pixels of the image being printed. The print medium is typically held stationary while the printheads complete a “print swath.” The print medium is then advanced and the carriage again moves across the print medium to print on the next portion of the medium.
Color ink jet printers commonly employ a plurality of printheads mounted in the print carriage to produce different colors. Each printhead contains ink of a different color, with commonly used colors including cyan, magenta, yellow, and black. These base colors are produced by depositing a drop of the required color onto a dot location. Secondary or shaded colors are formed by depositing drops of different colors on adjacent dot locations; the human eye interprets the color mixing as the secondary or shading, through well known optical principles.
Some ink jet printers use a fixer fluid, depending on the type of inks or the print medium being used, for example. Fixer fluids can be used to pretreat the print medium, causing the subsequently applied colored ink droplets to precipitate quickly. In still other ink jet printers, an overcoat fixer fluid is applied during the printing process after the colored inks have been applied to the print media. In such printers, one or more additional printheads are provided for depositing the fixer fluid.